1. Field of the Invention
This invention relates to apparatus for promoting settling of solids from waste water, and more particularly to an inlet for dissipating the energy of incoming liquid and solids flowing into a basin, and distributing a reduced-energy flow of the liquid and the solids near the top of the basin, such that as the liquid and the solids flow downwardly to flow channels of a clarifier section the energy of the liquid and the solids is reduced enough to avoid substantial interference with counterflowing of solids settling to the bottom of the clarifier section.
2. Discussion of Prior Clarifiers
Clarifiers remove certain materials and particles from liquid. These materials are generally suspended in the liquid and can be removed under the force of gravity when the velocity of the liquid is substantially reduced. Since these materials are generally solid and are said to "settle" out of the liquid, they are referred to as "settleable solids". Such settleable solids may include naturally occurring materials (e.g., clay, silts, sand and dirt), chemical precipitants and biological solids. The word "solids" as used herein to describe the present invention refers to such settleable solids.
Clarifiers are used, for example, in water and waste water treatment plants. In water treatment, the water drawn from a water supply has various non-settleable colloidal solids therein. When mixed with chemicals, the colloidal solids and chemicals agglomerate to form settleable solids. In waste water treatment, the solids include organic solids, among other wastes. Water and waste water are treated in clarifiers to remove such settleable solids, thereby making the water clear and suitable for use, reuse, or for further treatment, such as tertiary treatment. The word "liquid" as used herein to describe the present invention refers to water and waste water. When reference is made to both such liquid and such settleable solids carried by the liquid, the term "influent" is used.
An object of water and waste water clarifiers is to create a low flow velocity in each of many flow channels to promote maximum settlement of the solids to the bottom of the clarifiers. Clarifiers typically include a large natural detention basin. Early clarifier basins (e.g., ponds) simply had a very large bottom surface area relative to the flow velocity of the influent flowing into the basin or pond through one or more inlet pipes. However, the large area took up too much space (footprint) in crowded urban areas.
Therefore, man-made basins were provided with more efficient structures for settling the solids. For example, concrete rectangular basins have been provided with vertical baffles extending longitudinally and from above the surface of the liquid to points spaced from the bottom of the basin to define clarifier sections in the basins. Transverse to such longitudinal baffles, cross (or inlet) baffles have extended from above the surface of the liquid to a point close to the bottom. The inlet baffles force the liquid to enter the clarifier section near the bottom of the basin. The space between such a cross baffle and a front wall of the basin is referred to as an inlet section of the clarifier.
The clarifier sections are the volume in which settling of the settleable solids takes place. Such clarifier sections have been provided with tubes or flat plates mounted at fixed or variable angles relative to the surface of the liquid. Considering the plates, they form multiple thin liquid flow channels within the detention basin. The plates are used in an attempt to minimize the area (footprint) of the basin in which the settling of solids occurs while increasing settling velocities. The plates extend below the bottom of the vertical barriers. With the above-described cross baffles, the influent flows along the bottom of the basin and then upwardly between the plates of the clarifier sections. The intended flow velocities between the plates would allow sufficient time for most of the solids to settle onto the plates. Ideally, the solids settle within a thin counterflow of liquid and then flow down the plates, past the bottoms of the vertical barriers, downwardly below the bottoms of the plates, and then settle further downwardly onto the bottom of the detention basin for collection. As the solids settle onto the bottom, the downward counterflow of liquid joins inflowing influent (with the non-settled solids therein) which flows upwardly from the bottom of the basin into the flow channels. Ideally, the settling occurs and clarified liquid flows out of the clarifier section through openings between and at the top of the plates.
In some cases, the inlet pipe to the basin has been provided with a diffuser section to assist the vertical baffles in directing the flow of influent across the bottom of the inlet section of the basin toward the side walls of the basin. Also, some effort has been made to improve the plates or tubes of a clarifier section in an attempt to increase the settling efficiency (in terms of the parts per million of solids removed from liquid flowing at a given velocity through the clarifier section). However, it appears to Applicant that insufficient attention has been given to the dynamics of fluid flow in the clarifier basin. For example, the above-described flow of the influent along the bottom of the clarifier basin tends to stir up the settled solids before they can be removed from the basin (e.g., by a suction device). Also, the influent upflow opposite to the downward counterflow tends to entrain the settling solids in the inflow. Both of these conditions tend to lower the efficiency of the clarifiers.
Also, although distributor sections are used to supply influent along the length of a clarifier section, many clarifier designs also permit relatively high influent flow velocities to exist in the basin directly within the distributor sections. The high velocity liquid flows to bottom inlets of the flow channels of the clarifier sections. For example, some prior clarifiers have used large distribution pipes extending longitudinally in the basin to supply the influent longitudinally along the clarifier section. However, such pipes usually have small openings which form jets of influent. The jets flow at high velocity, are pointed downwardly toward the bottom of the plates of the clarifier section, and cause high velocity streams of the influent to enter the flow channels of the clarifier sections. Because such jets flow to the bottom of the basin below the clarifier section, the jets stir up the previously settled solids which join the incoming new settleable solids. Similarly, Schulz U.S. Pat. No. 4,957,628 issued Sep. 18, 1990 uses side manifolds to supply the influent to the sides of clarifier section. However, there are also small openings in such manifolds, and the resulting jets discharged therefrom directly enter the flow channels and interfere with establishing the necessary low flow velocity in the clarifier section.
Others have used a square or rectangular manifold connected to an inlet pipe that extends in the longitudinal direction through the front wall of the basin. The manifold extends perpendicular to the inlet pipe and has opposite ends thereof closed. The liquid and the solids flow from the manifold into the basin through inlet orifices cut into the bottom of the manifold. Again, jets of influent are directed downwardly across the front wall of the basin and onto the bottom of the basin for flow under the cross baffle to the bottom of the plates of the clarifier section.
Examples of flow resulting from other inlet designs include the inlet baffle shown in U.S. Pat. No. 5,101,849 to Richard issued Apr. 7, 1992. In a rectangular basin, an inlet pipe extends into the front wall of the basin and is connected to a sleeve. The sleeve supplies a flow of influent to a vertically extending hollow baffle having an upper end closed by the top of the basin and an open lower end. The influent is directed out of the open lower end toward the bottom of the basin.
In still other inlet designs, the inlet pipe to a rectangular basin enters high on the front wall of the basin, opposite to a flat front surface of the cross baffle at the front of the clarifier section. The influent flows directly onto that cross baffle, and in a turbulent flow transition is thereby diverted transversely across and downwardly along the cross barrier. This establishes a complex flow pattern including substantial eddy currents which return toward the inlet pipe.
In Applicant's analysis, (1) these methods of flowing the influent at relatively high velocities into the clarifier, and (2) the high velocity jets supplying influent directly to the clarifier sections, have the following effects: (a) detract from the efficiency of the operation of the plates of the clarifier sections, and (b) generally decrease the efficiency of the entire clarifier due, for example, to the mixing of the jets with previously settled solids.
In cylindrical tank clarifiers, some inlets have been secured to the top of the tank and direct the influent tangentially relative to the curved wall of the tank. For example, in U.S. Pat. No. 5,120,436 to Reichnet issued Jun. 9, 1992, an inlet pipe is tangential to a cylindrical clarifier basin which has a conical clarifier section below the inlet pipe. The influent appears to continue in circular or swirling paths as it flows into and then in flow paths defined by plates of the conical clarifier section. As a result, it appears that the flow velocity of the influent to the clarifier section is relatively high, which lowers the efficiency of the clarifier.
In another variation of a cylindrical clarifier, in U.S. Pat. No. 4,859,327 issued Aug. 22, 1989 to Cox, et al., a cylindrical tank is provided with a propeller mixer located near the periphery of the cylindrical wall. The mixer maintains a strong circular current in the tank.
Finally, in a fluidized bed mixer having a vertical open inverted conical mixing section, influent liquid has been caused to flow tangentially and swirl in an upwardly circular path to mix particles therein and form a blanket of particles.